Curable compositions

ABSTRACT

A two-component system for producing two or more different curable mixtures in which the first component A is common to each mixture and comprises: 
     1. a liquid epoxy 
     2. an acid anhydride hardener and 
     3. at least one filler 
     and the second component B is selected from two or more different components B, each of which comprises: 
     1. an accelerator, and optionally 
     2. a colourant, and optionally 
     3. a non-volatile solvent/extender for the accelerator 
     4. a flexibiliser for the epoxy-anhydride cure 
     5. a acid anhydride hardener.

The present invention relates to a two part system for producing acurable epoxy resin composition.

Epoxy resin systemis used for making cast products are conventionallysupplied as 1-, 2-, 3- or even 4- part compositions which are mixedimmediately before use. The most popular systems are 2-part systems, onepart containing the epoxy resin and the other part containing thehardener.

Various types of hardener are known, but when making moulded products,it is useful if the mixture of the two parts do not cure immediately,but had a useful life at the mixing temperature.

When processing to make a cast article, the resin is usually firstpre-heated in an oven at 40° C. to 100° C., e.g. about 90° C. Thehardener is then added and the mixture is then mixed under vacuum tode-aerate it. Typically the mixture will have a temperature of 65° C.and when using an acid anhydride hardener, have a useable life of about3 hours at 65° C.

A typical epoxy resin/anhydride casting resin system comprises about30-45% by volume of epoxy resin, 25-35% by volume of anhydride hardener,and 30-45% by volume of mineral filler, together with minor amounts ofcure accelerator and other additives.

For technical and cost reasons it is desirable to maximise the level ofmineral filler in the system. However, the achievement of high loadingsby the caster is complicated for various reasons.

The handling of mineral fillers presents health hazards and requires theskills and equipment available in a resin manufacturer's or formulator'splant but not normally in a casting plant.

Anhydride casting resin systems intended for rapid curing at 100°-200°C. do not usually have sufficient stability at ambient temperatures topermit manufacture and supply as filled single part products. Supply andstorage at low temperatures might overcome this problem but incursadditional costs.

With the normal basic resin: hardener mixing ratio being close to 1:1 itis not possible to accommodate the high level of total filler in theresin alone; such a mixture would be too intractable to process. Theresin can accommodate only about half as much filler as can the overallresin-hardener mixture.

Whereas manufacture and supply of a resin-filler premix is a simple andcommonly adopted technique, prefilled anhydride hardeners are subject tosever filler settlement and hard packing because of the low viscosity ofthe anhydride itself. Furthermore the separate filling of both resin andhardener is inefficient because it involves an additional processingstep with concomitant costs. Moreover, if the caster requires numerouscolour variants then economies of scale in the manufacture of pre-filledresins are sacrificed. The cost is increased further if the resins areto be handled in bulk since a number of storage containers will beneeded.

It is apparent from the above that great efficiencies could be achievedif the epoxy resin system could be supplied in the form of a two partcomposition wherein one part constituted less than 25% and preferablyless than 10% of the final composition and incorporated the variableelements, principally the colour.

We have now developed such a system wherein both parts display adequatestability for storage and transport at normal ambient temperatures.

Accordingly the present invention provides a two-component system forproducing two or more different curable mixtures in which the firstcomponent A is common to and comprises 75 to 99.8% by volume of eachmixture and comprises:

1. a liquid epoxy resin

2. an acid anhydride hardener and

3. at least one filler

and the second component B which comprises 0.2 to 25% by volume of eachmixture is selected from two or more different components B, each ofwhich comprises:

1. an accelerator, and optionally

2. a colourant

3. a non-volatile solvent/extender for the accelerator

4. a flexibiliser for the epoxy-anhydride cure

5. ac acid anhydride hardener.

Either one or both of components A and B may also contain other minoradditives.

Component A may be made by mixing the components in any order and at anytemperature subject to two criteria, namely that the mixture viscositycan be accommodated by the mixer and that the temperature issubstantially below the temperature of onset of the cure reaction. Amargin of 50° C. is widely regarded as a desirable margin of safety inthe latter respect

A preferred process for producing a formulation containing a largeamount of filler is to charge warm epoxy resin to a vessel, mix in anyantioxidant and other minor additives, then about half of the filler,then all the hardener then, finally, all the remaining filler. Thetemperature may be allowed to fall as the filler and hardener are added.

Suitable epoxides include polyglycidyl esters, polyglycidyl esters, andcycloaliphatic epoxides.

Epoxides which may be employed are preferably those containing, onaverage, more than one group of formula ##STR1## directly attached to anatom or atoms of oxygen or nitrogen, where R¹ denotes a hydrogen atom ora methyl group.

As examples of such epoxides may be mentioned polyglycidyl andpoly(beta-methylglycidyl)esters obtainable by reaction of a compoundcontaining two or more carboxylic acid groups per molecule withepichlorohydrin, glycerol dichlorohydrin, or beta-methylepichlorohydrinin the presence of an alkali. Such polyglycidyl esters may be derivedfrom aliphatic polycarboxylic acids, e.g. oxalic acid, glutaric acid,adipic acid, pimelic acid, suberic acid, sebacic acid, or dimerised ortrimerised linoleic acid; from cycloaliphatic polycarboxylic acids suchas tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid,hexadrophthalic acid, and 4-methylhexahydrophthalic acid; and fromaromatic polycarboxylic acids such as phthalic acid, isophthalic acid,and terephthalic acid.

Further examples are polyglycidyl and poly(beta-methylglycidyl)ethersobtainable by reaction of a compound containing at least two freealcoholic hydroxyl and/or phenolic hydroxyl groups per molecule with theappropriate epichlorohydrin under alkaline conditions or, alternatively,in the presence of an acidic catalyst and subsequent treatment withalkali. These ethers may be made from acyclic alcohols such as glycol,diethylene glycol, and higher poly(oxyethylene)glycols, propane-1,2-dioland poly(oxypropylene)glycols, propane-1,3-diol, butane-1,4,poly(oxytetramethylene) glycols, pentane-1,5-diol, hexane-1,6-diol,hexane-2,4,6-triol, glycerol, 1,1,1-trimethylol-propane,pentaerythritol, sorbitol, and polyepichlorohydrins; from cycloaliphaticalcohols such as resorcitol, quinitol, bis(4-hydrocycyclohexyl)methane,2,2-bis(4-hydroxycyclohexyl)propane, and1,1-bis(hydroxymethyl)cyclohex-3-ene; and from alcohols having aromaticnuclei, such as 2,4-(dihydroxymethyl)benzene. They may also be made frommononuclear phenols, such as resorcinol and hydroquinone, and frompolynuclear phenols, such as bis(4-hydroxyphenyl)methane,4,4'-dihydroxydiphenyl, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)-propane,2.2-bis(3,5-dibromo-4-hydroxyphenyl)propane, and novalaks formed fromaldehydes such as formaldehydes, acetaldehyde, chloral, andfurfuraldehyde, with phenols such as phenol itself, and phanolsubstituted in the ring by chlorine atoms or by alkyl groups eachcontaining up to nine carbon atoms, such as 4-chlorophenol,2-methylphenol, and 4-tert-butylphenol.

Epoxides in which some or all of the epoxide groups are not terminal mayalso be employed, such as vinylcyclohexane dioxide, limonene dioxide,dicyclopentadiene dioxide, 4-oxatetracyclo 6,2.1.0²,5.0³,5 !undec-9-ylglycidyl ether, the bis(4-oxatetracyclo 6.2.10²,7.0³,5 !undec-9-ether ofethylene glycol, 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate and its 6,6¹ dimethyl derivative, thebis(3,4-epoxycyclohexane-carboxylate) of ethylene glycol,3-(3,4-epoxycyclohexyl)-8.9-epoxy-2,4-dioxaspire 5,5!undecane, andepoxidised butadienes or copolymers of butadiene with ethyleniccompounds such as styrene and vinyl acetate.

Epoxide resins having the 1,2-epoxide groups attached to different kindsof hetero atoms may be employed, e.g. the glycidyl ether-glycidyl esterof salicylic acid. If desired, a mixture of epoxide resins may be used.

Preferred epoxides are polyglycidyl esters, polyglycidyl esthers of2,2-bis(4-hydroxyphenyl)propane, of bis(4-hydroxyphenol)-methane or of anovalak formed from formaldehyde and phenol, or phenol substituted inthe ring by one chlorine atom or by one alkyl hydrocarbon groupcontaining from one to nine carbon atoms, and having a 1,2-epoxidecontent of at least 0.5 equivalent per kilogram, and3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate.

The epoxy resin should be pure enough and have a low hydroxyl content soas to give stability in the presence of the hardener.

The hardener is an acid anhydride. Suitable anhydrides are eitherliquid, or solids. Anhydride hardeners suitable for use includemethyltetrahydrophthalic anhydrides, hexahydrophthalic anhydride,methylhexahydrophthalic anhydrides, methylendomethylenetetrahydrophthalic anhydrides, tetrahydrophthalic anhydride,phthalic anhydride, alkenesuccinic anhydrides, maleic anhydride,succinic anhydride, glutaric anhydride or fumaric anhydride. Mixtures ofsuch anhydrides may be used advantageously to depress the individualmelting point and thereby repress crystallisation of anhydride outcomponent A.

The anhydride hardener should have a low acid content in order to ensurestability of the formulation.

A wide range of fillers may be used, both fine and coarse particles. Thefiller may be inorganic such as china clay, calcined clay, quartz flour,cristobalite, chalk, precipitated calcium carbonate, mica powder, glasspowder, glass beads, powdered glass fibre, aluminium oxide and magnesiumhydroxide, or organic such as powdered poly(vinylchloride), nylon,polyethylene, polyester or cured epoxy resin. Flame retardant fillerssuch as trihydrated aluminia may also be used.

Mixtures of fillers may be used. For example in order to givegranite-like effect in a moulded product mixture of calcined china clayand black mica of relatively large particle size may be used, forinstance about 0.5 mm.

The filler may also have its surface treated with a silane ororganotitanate coupling agent

In general fillers having a particle size of from 1 to 10,000 micronsmay be used, depending on the desired effect. The amount of filler maybe from 20-65% by volume of the total mixture, preferably from 40-60% byvolume.

In order to assist in preventing any settling of the filler, athixotropic agent may be added, provided that the final compositionexhibits sufficient fluidity to be transferred through pipes and intomoulds by application of pressures of less than 5 bar.

Suitable thixotropic agents include highly dispersed silicas, bentoniteand silicates or organic compounds such as hydrogenated castor oil. Itmay be used in amounts of from 0.5 to 10 parts by weight per 100 partsby weight of epoxy resin, preferably 1 to 3 parts by weight.

Each component B may be made by mixing the components in any order andat any temperature.

The inclusion of a solvent/extender and/or acid anhydride hardenerenables solid accelerators to be used and permits the ratio of compoundB to component A to be increased to facilitate the use of commerciallyavailable meter-mixing equipment or to avoid the need for sensitiveweighing equipment.

A wide range of accelerators may be used as they do not need to bestable in the epoxy resin.

Examples of suitable accelerators for component B are tetiary amines,di-azabicycloundecene or imadazoles salts thereof with phenols or acids,zinc octoate, stannous octoate, alkali metals alkoxides, quaternaryammonium or phosphonium compounds and latent accelerators.

Suitable quaternary ammonium and phosphonium compounds include halidesand acetates such as tetramethylammonium chloride, tetraethylammoniumchloride, benzyltrimethylammonium chloride, dodecylbenzyldiethylammoniumchloride, tetramethylammonium acetate, tetrabutylphosphonium bromide,ethyltriphenylphosphonium chloride and methyltriphenyl phosphoniumbromide.

Suitable latent accelerators include boron trihalide complexes ofalkyldimethylamines having 1 to 18 carbon atoms in the alkyl groups, forexample trimethylamine or n-decyldimethylamine or ofaralkyldimethylamines, for example benzyldimethylamine. The borontrihalide is preferably boron trichloride. Other suitable acceleratorsinclude complexes of heavy metal carboxylates with imidazoles, ornon-latent amine or imidazole accelerators protected bymicroencapsulation in heat sensitive barriers or by adsorption intomolecular sieves.

The colourant may be a dyestuff or an organic or inorganic pigment ormixtures thereof.

Suitable non-volatile solvents/extenders for the accelerator includehigh-boiling liquid hydrocarbons, phthalate ester plasticisers, cycliclactones or lactams, mono- or polyfunctional phenols.

Phenol novolac resins, high boiling point glycol- or polyglycol ethers.

Suitable flexibilisers include polyols, both aliphatic and cyclic orplycarboxylic acids. Such polyols and polycarboxylic acids may consistof hydroxyl- or carboxyl- terminated polyesters respectively.Polycarboxylic acid flexibilisers may be formed in-situ by compoundingpolyols and carboxylic anhydrides into Component B and allowing these toreact.

Other additives conventionally employed in moulding resin compositionsmay also be included on one or both of components A and B. Examples ofsuch additives are fibres such as glass and carbon fibres, flameretardants, antioxidants, light stabilisers, UV absorbers, surfactants,anti-foaming agents, toughening agents such as rubbers and core-shellpolymers, and other stabilisers such as lower carboxylic acids.

Examples of suitable antioxidants include alkylated monophenols,alkylthiomethylphenols, hydroquinones and alkylated hydroquinones,hydroxylated thiodiphenyl ethers, alkylidenebisphenols, O-, N- andS-benzyl compounds, hydroxybenzylated malonates, hydroxybenzylaromatics, triazine compounds, benzylphosphonates, acylaminophenols,esters and amides of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionicacid, esters of β-(5-tert-butyl-4-hydroxy-3-methylphenyl)propionic acid,esters of β-(3,5-dicyclohexyl-4-hydroxyphenyl)propionic acid and estersof 3,5-di-tert-butyl-4-hydroxyphenyl acetic acid.

Examples of suitable UV absorbers and light stabilisers include2-(2'-hydroxyphenyl)benzotriazoles, compounds, sterically hinderedamines, oxalic acid diamides and 2-(2-hydroxyphenyl)-1,3,5-triazines.

The system of the present invention may be used to make moulded articlesby what is called Automatic Pressure Gelation Process (APG). In thisprocess which is described for example in GB 1323343 and EP 0333456 anepoxy resin and a curing agent are mixed at a temperature at which theyare liquid, usually 40-70° C. The mixture is then passed, under slightpressure, into a mould which is at a high enough temperature for gellingand curing to take place. Further mixture is supplied to the mould underthe application of pressure to compensate for shrinkage of thecomposition until the composition has set.

In order to cure the composition, components A and B are mixed togetherand then passed to a mould which is at a high enough temperature to curethe composition, e.g. at a temperature of from 100° to 200° C. Theactual temperature needed depends on the nature of the compound used.

Components A and B are mixed in a suitable ratio to enable completecuring to occur. This usually means providing 0.5-1.1 mol of anhydrideand optionally 0.1-0.25 mol of acid or polyol per mol of epoxy. Theamount of accelerator may be up to 5 parts by weight preferably 0.2 to0.8 parts by weight per 100 parts by weight of liquid epoxy resin.

To achieve this component A is used in an amount of 75 to 99.8% byvolume and component B in an amount of 0.2 to 25% by volume.

The polyol or polyacid acts not only as a carrier for the acceleratorand colourant but also prevents decarboxylation of anhydride during hightemperature gelation.

The formulations used in the present invention allow the mouldingprocess to be carried out at high temperatures of up to 200° C. withoutdecarboxylation. This allows for fast production. The moulded productscan also be demoulded easily because they soon become tough enough oncethe curing has started. The final moulded products also have very goodmechanical and electrical insolation properties and chemical resistance.

The process of the invention may be used for the production of mouldingshaving thin or thick walls (cross sections). It is also particularlysuitable for the production of mouldings having a large surface area, atleast one large linear dimension or a complex shape. The process may beused, for instance, in the moulding of domestic sanitary ware such assinks, bathsm shower trays and basins, sheet slabstock for use in theproduction of articles such as domestic worktops, chemically resistantcontainers such as tanks and parts such as pumps, valves and pipes forhandling corrosive fluids and impact-resistant mouldings for use in carsand other vehicles, and electrical applications.

A manufacturer of moulded products can operate according to theinvention by having one large contained for component A and a number ofsmall containers for different components B. The desired product car, bemade by simply selecting the appropriate component B for mixing withcompound A, e.g. to produce a desired colour. No storage problems ariseas both components A and B are stable for 6-12 months at roomtemperature.

The invention is illustrated by the following Examples.

EXAMPLE 1

Viscosity vs time measurements were carried out at 25° C. on component Acomprising 18.1% liquid Bisphenol A epoxy resin, 14.9% anhydridehardener blend, 66.1% silica flour filler and 0.9% antisettlement agent.Measurements were made using a Brookfield DV 11 viscometer with spindle7 at 10 rpm. The viscosity remained constant for the test period of 70days at 11 to 11.5 Pas.

EXAMPLE 2

Component A is made from 54.2% liquid Bisphenol A epoxy resin and 45.8%anhydride hardener blend (comprising 30% methylhexahydrophthalicanhydride and 70% hexahydrophthalic anhydride).

Component A¹ was prepared on one day and component A¹¹ was prepared 30months later.

Component B is made from 36.6% benzyltriethylammonium chloride and 63.4%ethylene glycol.

Gel times were measured on the day component A¹¹ was made using ahotblock at 150° C. and a Techne gel timer. Measurements were made on7.5 g of a mixture of 100 parts by weight component A¹ or A¹¹ and 2.2parts by weight of component B.

A¹ +B 3 mins at 150° C.

A¹¹ +B 2 mins at 150° C.

It can be seen that there is little difference in the gel times of thetwo mixtures and shows the stability of the base matrix resin.

We claim:
 1. A multi-part system for producing curable mixturescomprising at least a first mixture and a second mixture and/or a thirdmixture, wherein the first mixture consists of a component A and thesecond and third mixtures consist of a component B as follows, in whichthe component A is present at 75 to 99.8% by volume of said curablemixture and comprises:A1. a liquid epoxy A2. an acid anhydride hardenerand A3. at least one fillerand the component B is present at 0.2 to 25%by volume of said curable mixtures, wherein the second mixture containscomponent B in different volumetric amounts or different combinations ofcomponents B1 through B5 than component B in the third mixture, whereincomponent B is a mixture comprising: B1. an accelerator, and optionallyB2. a colourant, and optionally B3. a non-volatile solvent/extender forthe accelerator B4. a flexibiliser suitable for epoxy-anhydride curesystems and B5. an acid anhydride hardenerand optionally at least one ofsaid components B contains a colourant.
 2. A system as claimed in claim1 in which the liquid epoxy resin is a polyglycidyl ester, polyglycidylether or cycloaliphatic epoxide.
 3. A system as claimed in claim 1 inwhich the acid anhydride hardener has a low acid value to ensure storagestability.
 4. A system as claimed in claim 1 in which the filler has aparticle size of from 1 to 10000 microns.
 5. A system as claimed inclaim 1 in which component A comprises 20-65% by volume of filler.
 6. Asystem as claimed in claim 1 in which the accelerator is a tertiaryamine or imidazole or di-azabicycloundecene or a salt thereof with anacid or phenol, zinc octoate, an alkali metal alkoxide, a quaternaryammonium or phosphonium compound or a latent accelerator.
 7. A system asclaimed in claim 1 in which the non-volatile solvent/extender is a highboiling hydrocarbon, a phthalate ester plasticiser, cyclic lactone orlactam, mono- or poly-functional phenol, novalak resin, a high boilingpoint glycol or polyglycol ether.
 8. A system as claimed in claim 1 inwhich the flexibiliser is an aliphatic or cyclic polyol or apolycarboxylic acid.
 9. A system as claimed in claim 1 in which one orboth of components A and B also contain one or more additivesconventionally employed in moulding resin compositions selected from thegroup of fibers, flame retardants, antioxidants, light stabilizers,ultraviolet light absorbers, surfactants, anti-foaming agents,toughening agents, stabilizers and mixtures thereof.
 10. A process formaking a cured composition which comprises mixing at least a firstmixture and a second mixture and/or a third mixture for producingcurable mixtures, wherein the first mixture consists of a component Aand the second and third mixtures consist of a component B as follows,in which the first component A is present at 75 to 99.8% by volume eachof said curable mixture and comprises:A1. a liquid epoxy A2. an acidanhydride hardener and A3. at least one fillerand the component B ispresent at 0.2 to 25% by volume of said of curable mixtures, wherein thesecond mixture contains component B in different volumetric amounts ordifferent combinations of components B1 through B5 than component B inthe third mixture, wherein component B is a mixture comprising: B1. anaccelerator, and optionally B2. a colourant, and optionally B3. anon-volatile solvent/extender for the accelerator B4. a flexibilisersuitable for epoxy-anhydride cure systems and B5. an acid anhydridehardenerand optionally at least one of said components B contains acolourant and then passing at least one of said curable mixtures to amould at a high temperature which is high enough to cure thecomposition.
 11. A process as claimed in claim 10 in which components Aand B are mixed and passed under slight pressure to a mould which is ata high enough temperature for curing to take place and where furthermixture supplied under pressure to compensate for shrinkage of thecomposition.
 12. A multipart system according to claim 1 wherein atleast one said components B contains a colourant.
 13. A multipart systemaccording to claim 1 wherein only one of said components B contains acolourant.
 14. A multipart system according to claim 10 wherein at leastone said components B contains a colourant.
 15. A multipart systemaccording to claim 10 wherein only one of said components B contains acolourant.